1. Technical Field
The present invention generally relates to the surface treatment of biomedical devices such as contact lenses and medical implants.
2. Description of the Related Art
Ophthalmic devices such as contact lenses made from, for example, silicone-containing materials, have been investigated for a number of years. Such materials can generally be subdivided into two major classes, namely hydrogels and non-hydrogels. Hydrogels can absorb and retain water in an equilibrium state whereas non-hydrogels do not absorb appreciable amounts of water. Regardless of their water content, both non-hydrogel and hydrogel contact lenses tend to have relatively hydrophobic, non-wettable surfaces.
Those skilled in the art have recognized the need for modifying the surface of contact lenses so that they are compatible with the eye. It is known that increased hydrophilicity of a contact-lens surface improves the wettability of the contact lenses. This, in turn, is associated with improved wear comfort of the contact lens. Additionally, the surface chemistry of the lens can affect the lens's susceptibility to deposition, particularly the deposition of proteins and lipids from the tear fluid during lens wear. Accumulated deposition can cause eye discomfort or even inflammation. In the case of extended-wear lenses, the surface is especially important, since extended-wear lenses must be designed for high standards of comfort over an extended period of time, without requiring daily removal of the lenses before sleep. Thus, the regimen for the use of extended-wear lenses would not provide a daily period of time for the eye to rest or recover from any discomfort or other possible adverse effects of lens wear during the day. Accordingly, it is highly desirable that contact lenses be as comfortable as possible for wearers.
Various patents disclose the attachment of hydrophilic or otherwise biocompatible polymeric chains to the surface of a contact lens in order to render the lens more biocompatible. For example, U.S. Pat. No. 5,652,014 discloses amination of a substrate followed by reaction with other polymers, such as a polyethylene oxide star molecule or a sulfated polysaccharide. One problem with such an approach is that the polymer chain density is limited due to the difficult of attaching the polymer to the silicone substrate.
U.S. Pat. No. 5,344,701 discloses the attachment of oxazolinone or azlactone monomers to a substrate by means of plasma. The invention has utility in the field of surface-mediated or catalyzed reactions for synthesis or site-specific separations, including affinity separation of biomolecules, diagnostic supports and enzyme membrane reactors. The oxazolinone group is attached to a porous substrate apparently by reaction of the ethylenic unsaturation in the oxazolinone monomer with radicals formed by plasma on the substrate surface. Alternatively, the substrate can be coated with monomers and reacted with plasma to form a cross-linked coating. The oxazolinone groups that have been attached to the surface can then be used to attach a biologically active material, for example, proteins, since the oxazolinone is attacked by amines, thiols, and alcohols.
U.S. Pat. Nos. 5,352,714 and 5,364,918 disclose the use of oxazolinone monomers as internal wetting agents for contact lenses, which agents may migrate to the surface of the contact lens.
U.S. Pat. No. 5,804,318 discloses lubricious coatings for reducing the coefficients of friction of surfaces on medical devices, including hydrophilic copolymers containing some monomers having pendant tertiary amine functionality. The hydrogel coatings are covalently bondable to epoxy functionalized surfaces on the medical equipment.
It would be desirable to provide improved biomedical devices having an optically clear, hydrophilic coating on the surface thereof that renders the device more biocompatible. It would also be desirable to form a coating for a biomedical device such as a contact lens that is lubricious, highly wettable and more comfortable to wear for a longer period of time. In addition, it would be desirable to provide a coating with these properties that can be readily renewed to restore its properties to an as-new state.